At present, the steel rails widely used in railway mostly are made of eutectoid pearlitic steel, characterized by good match in strength and toughness, moderate performance indexes and as such. However, following the continuous increase of traffic density and axle load of freight trains, high requirements are set for the service performance of railway rails. The fast abrasion at the wheel-track contacting locations has gradually become a main factor affecting the service life of heavy rails, particularly the rails at the curves with a small radius. For this reason, the R&D personnel in this field have always been dedicated to developing new steel rail products with good abrasion resistance as well as good contact fatigue resistance and other comprehensive performance indexes to meet the need of railway construction.
The research discovers there are two methods which can meet all of the above requirements: one is to further raise the carbon content of steel rails, add an appropriate amount of alloying elements, give full play to the role of carbon in enhancing abrasion resistance of steel rails and provide better abrasion resistance and contact fatigue resistance for steel rails through a post-rolling cooling process; the second one is to use bainite steel rails with high alloy content, obtain bainite steel rails with good abrasion resistance also through controlling post-rolling cooling process and raise abrasion resistance while giving full scope to their contact fatigue resistance. As proved in practice, due to high alloying cost and a complex production process of bainite steel, the product is unstable in performance and does not possess the condition of mass popularization and application, while although high-carbon hypereutectoid steel rail can significantly improve the abrasion resistance of steel rail through raising carbon content of the steel rail, due to high carbon content, secondary cementite will be precipitated with priority on austenite grain boundary during continuous cooling of the steel rail with which the austenite forms pearlite after rolling and the secondary cementite is distributed in a net shape along the original austenite grain boundary. As the hard phase and strengthening phase of steel, the secondary cementite unquestionably raises hardness and abrasion resistance of the steel, but its adverse effect is non-negligible too: under the impact of wheel stress, it is liable that micro-cracks are formed at the cementite location and spread continuously along its net shape, finally result in peeling, chipping, oblique cracks and other fatigue damages at the contact locations and even induce rail breakage, imposing an extreme hidden danger to railway transport safety.
Reducing precipitation of secondary cementite in a method for heat treatment of high-carbon hypereutectoid steel rail is a key to the production of steel rails with excellent abrasion resistance and fatigue resistance. Therefore, it is in urgent need in this field to develop a method for heat treatment of high-carbon hypereutectoid steel rail, which can reduce precipitation of secondary cementite.